After an IC chip has been mounted on a lead frame chip carrier, and electrically connected to the leads thereof, it is often packaged in encapsulating material. Such packaged chip-containing lead frames are shown in, for example, the following U.S. Pat. Nos. 4,331,831; 4,301,464; 4,298,883; 4,264,917; 4,214,364; 4,132,856; 4,124,864; 4,079,511; 3,978,516; 3,793,474; 3,684,464; 3,659,821; 3,611,061; 3,436,810; and U.S. patent application Ser. No. 584,080; filed Feb. 27, 1984, the teachings of which are herein incorporated by reference.
As pointed out in the above, the lead frames are usually made by stamping or etching metal strips. Where the manufactured quantities are sufficiently great, stamping is preferred because of its lower cost.
As the circuits on the chips become more complex, a greater number of leads per lead frame is required. This complicates the stamping operation. Stamping is carried out in progressive dies; that is, a metal strip is fed through a stamping press having successive punch and die sets at a number of stations, where successive stamping operations are carried out. For example, a lead frame having 68 leads would require about 15 to 20 stamping stations and about 140 to 150 cuts. As the number of required stamping stations and cuts increases, the difficulty in maintaining adequate quality of the stamped lead frames also increases.
As taught in the above-mentioned patent application Ser. No. 584,080, these assemblies are prepared by securely attached a plurality of lead-ins to a base and then fixing an integrated circuit chip on the base relative to the lead-ins. Appropriate electrical connections are made between the lead-ins and the chip and a cover is placed thereover and fixed thereto. The cover contains a central depression to accommodate the chip and is provided with an annular groove, semi-cylindrical in cross-section, for receiving a fluid sealant. The base is provided with a matching groove and either the cover or the base, usually the cover, is provided with apertures which communicate with the groove so the sealant material can be injected into the groove. The injection of the sealant material requires an extra processing step that adds to the cost of the package.